Missing Backflow Preventer Main Control Valve and Water Leak

I noticed my water bill has been about 4 times higher that the same time last year (don't run sprinklers in winter). I checked the water meter and timed it for an hour. It showed 12 gallons used even with nothing on using water in the home. I checked all the toilets and they operate normally. I assumed it to be a leak in a sprinkler line. I have had leaks in the past and they were leaky valves and one burst underground pipe, all fixed by professionals with no issues reported to me. The sprinkler was installed when the home was built in Sept 2008.

So I called a reputable local sprinkler repairman and he comes out. He cannot find any evidence of a leak (mud, extra green grass etc.) I should note that my small residential lot is pretty much a solid piece of shale/rock. I remember watching the sprinkler being installed and they had to use jack hammers to trench. Same for installation of the trees.

This repairman also says he cannot find the back flow preventer and master control valve so he can at least shut the sprinkler system down until we can find the leak. I see my neighbors house and the valve is right up front in a clearly visible box. Mine is nowhere to be found.

I thought I might be able to trace one of the supply lines from a valve back to the main water source but after several hours I gave up. Just too much rock to get through.

I called the city out to investigate and they said there was also supposed to be a customer shut off valve on the house side of the water meter by which you can shut off water to the house....they were not able to locate that either.

If you have a master valve, you can trace the wire right to the valve using a wire locator. The back flow's probably in a box right next to it. Maybe call around and find a guy who has experience using a locator. You obviously need a different guy to look.

Do you have a basement? If so look down there.

Your yard sounds like a nightmare being all rock. Filling a trench with rock on top of a sprinkler line can damage it.

Check your toilets and make sure one's not constantly running.

Check everything inside. Water heater...

Maybe one of your garden hoses isn't shut off all the way.

Is your main line under the slab floor of your house? Sometimes they leak under there and you don't see a wet spot for many months.

As a last resort you can hire a leak detector specialist. They're VERY expensive. They'll charge you hundreds of dollars or more just to point where there leak is and they drive away. Someone else has to fix it. But they're very accurate. These guys pinpointed a leak at my customers house 4 feet under the driveway.